Multiple-stage desulfurization of black oil

ABSTRACT

DESULFURIZATION OF HYROCARBONACEOUS BLACK OIL IS EFFECTED INA PLURALITY OF INDIVIDUAL CONVERSION ZONES. THE FIRST ZONE, CONTAINING A CATALYTIC COMPOSITE OF AN ALUMINA-CONTAINING CARRIER MATERIAL, A ZINC COMPONENT AND A GROUP VI-B COMPONENT, FUNCTIONS TO PRODUCE A HYDROCARBON STREAM CONTIANING FROM 1.0% TO ABOUT 2.0% BY WEIGHT OF SULFUR, AND PREFERABLY FROM 1.35% TO ABOUT 1.65% BY WEIGHT. THE SUBSEQUENT CONVERSION ZONE, CONTAINING A CATALYTIC COMPOSITITE OF A SILICEOUS CARRIER MATERIAL, A GROUP VIII METAL COMPNENT AND A GROUP VI-B METAL COMPONENT, EFFECTS FUTHER DESULFURIZATION TO A LEVEL LESS THAN ABOUT 1.0% BY WEIGHT.

United States Patent M 3,649,525 MULTIPLE-STAGE DESULFURIZATION 0F BLACK OIL Lee Hilfman, Prospect Heights, [1]., assignor to Universal Oil Products Company, Des Plaines, 111. No Drawing. Filed Nov. 6, 1969, Ser. No. 874,697 Int. Cl. (110g 23/02, 31/14 US. Cl. 208-210 6 Claims ABSTRACT OF THE DISCLOSURE Desulfurization of hydrocarbonaceous black oil is effected in a plurality of individual conversion zones. The first zone, containing a catalytic composite of an alumina-containing carrier material, a zinc component and a Group VI-B component, functions to produce a hydrocarbon stream containing from 1.0% to about 2.0% by weight of sulfur, and preferably from 1.35% to about 1.65% by weight. The subsequent conversion zone, containing a catalytic composite of a siliceous carrier material, a Group VIII metal component and a Group VI-B metal component, effects further desulfurization to a level less than about 1.0% by weight.

APPLICABILITY OF INVENTION Desulfurization is a process well known and thoroughly described in petroleum refining technology, and the literature relating thereto is replete with references directed to suitable desulfurization catalysts, methods and techniques of catalyst manufacture and the various operating techniques employed while effecting the desulfurization process. Although desulfurization connotes the destructive removal of sulfurous compounds, through conversion thereof into hydrogen sulfide and hydrocarbons, it is often included in the broad term hydrorefining. Hydrorefining processes are elfected at operating conditions *which promote denitrification and desulfurization primarily, and asphaltene conversion, non-distillable hydrocarbon conversion, hydrogenation and hydrocracking to a somewhat lesser extent. In other words, the terms hydrorefining and desulfurization are generally employed synonymously to allude to a process wherein a hydrocarbonaceous feed stock is cleaned-up, in order to prepare a charge stock suitable for utilization in subsequent hydrocarbon conversion, or to result in a product having an immediate utility, such as fuel oil containing less than 1.0% by weight of sulfur. Hydrorefining is further characterized in that some conversion into lower-boiling hydrocarbon products is effected.

Catalytic composites which are specifically intended to be used in a process for hydrorefining hydrocarbonaceous material, and particularly residual stocks or black oils, traditionally consist of an element chosen from the Irongroup metals, especially nickel or cobalt, in combination with a metal component from the metals of Group VI-B, particularly molybdenum or tungsten. In general, preferred metal components are nickel and molybdenum, or nickel and tungsten, and these components are generally combined with a porous carrier material which is either amorphous, or zeolitic in nature. Ample evidence may be found in the literature to indicate that the nickel com- 3,649,525 Patented Mar. 14, 1972 ponent, or cobalt component, while present in a significantly lower concentration, materially contributes to the activity of these catalyst. Notwithstanding the fact that these catalysts exhibit an acceptable high initial activity with respect to desulfurization, they also serve to dehydrogenate heavy hydrocarbons, and the high molecular weight species in black oils are easily subject to dehydrogenation which inherently leads to rapid excessive coke formation. Most black oils contain sulfurous compounds in excess of 3.0% by weight, as sulfur, and dehydrogenation is favored by the equilibrium at the operating conditions necessary to result in a product having an acceptable sulfur level, generally considered to be 1.0% by weight or less.

The present invention is directed toward a combination process for effecting the desulfurization of petroleum crude oils, atmospheric tower bottoms products, vacuum tower bottoms products, heavy cycle stocks, crude oil residuum, topped crude oils, the heavy hydrocarbonaceous oils extracted from tar sands, etc. Petroluem crude oils and the heavier hydrocarbon fractions and/or distillates obtained therefrom, particularly heavy vacuum gas oils, oils extracted from tar sands, and topped or reduced crudes, contain nitrogenous and sulfurous compounds in exceedingly large quantities, the latter generally exceeding about 3.0% by weight. In addition, such heavy hydrocarbon fractions, commonly referred to as black oils, contain large quantities of organo-metallic contaminants, principally containing nickel and vanadium, and heptane-insoluble asphaltenes. Specific examples of the black oils, illustrative of those to which the present scheme is applicable, include a vacuum tower bottoms product having a gravity of 7.1 API, containing 4.05% by weight of sulfur and 23.7% by weight of asphaltics; a topped Middle-east Kuwait crude oil, having a gravity of 11.0 API, containing 10.1% by weight of asphaltenes and 5.20% by weight of sulfur; and, a vacuum residuum having a gravity of about a 8.8 API, containing 3.0% by weight of sulfur, 4,300 p.p.m. by weight of nitrogen and having a 20.0% volumetric distillation temperature of about 1055 F.

OBJECTS AND EMBODIMENTS A principal object of the present invention is to provide a process for effecting the desulfurization of hydrocarbonaceous material. A corollary objective resides in a multiple-stage process for desulfurizing hydrocarbonaceous material characterized as black oil.

Another object is to provide a desulfurization process which improves the stibility of the traditional catalysts containing nickel and molybdenum, or cobalt and molybdenum.

Therefore, in one embodiment, the present invention relates to a combination process for producing a hydrocarbon stream containing less than about 1.0% by weight of sulfur from a higher-boiling, sulfurous charge stock containing more than 2.0% by weight of sulfur, which process comprises the steps of: (a) reacting said charge stock and hydrogen, at a first set of desulfurizing conditions selected to convert sulfurous compounds into hydrogen sulfide and a first hydrocarbon stream containing from 1.0% to about 2.0% by weight of sulfur, and in contact with a first catalyst of a composite of an alumina-containing carrier material, a zinc component and a Group VI-B metal component; and, (b) reacting at least a portion of said first hydrocarbon stream and hydrogen, at a second set of desulfurizing conditions selected to convert sulfurous compounds into hydrogen sulfide and a second, lower-boiling hydrocarbon stream containing less than about 1.0% by weight of sulfur, and in contact with a second catalyst of a composite of a siliceous carrier material, a Group VIII metal component and a Group VI-B metal component.

Other objects and embodiments of my invention relate to additional details regarding the preferred catalytic ingredients, the concentration of components within the catalytic composite, preferred processing techniques and similar particulars which are hereinafter given in the following, more detailed summary. One such embodiment relates to preferred operating conditions wherein the first set of desulfurizing conditions includes a maximum catalyst bed temperature in the range of 600 F. to about 900 F., while said second set of desulfurizing conditions includes a maximum catalyst bed temperature in the range of about 550 F. to about 850 F.

SUMMARY OF INVENTION My investigations in the area of desulfurization, particularly black oils, in regard to catalyst activity and stability have confirmed the known effect induced by a nickel component, or cobalt component in combination with a molybdenum component. With respect to activity, defined as the maximum catalyst bed temperature (all other conditions being equal) required to achieve initially a product sulfur level of by weight, a nickelmolybdenum catalyst is slightly more active than a cobaltmolybdenum catalyst, both of which are substantially more active than a catalyst containing only molybdenum. To illustrate, while processing a black oil at 2,000 p.s.i.g., the nickel-molybdenum catalyst required a maximum catalyst bed temperature of 718 F., the cobalt-molybdenum catalyst required a temperature of 722 F., whereas the molybdenum catalyst required a temperature of 784 F. In regard to catalyst stability, however, the trend strikingly reverses itself, with a molybdenum catalyst being significantly more stable than either a cobalt-molybdenum, or nickel-molybdenum catalyst. With catalyst stability being defined as the temperature increase, F., per barrel of fresh feed processed per pound of catalyst disposed in the reaction zone F./b.p.p.), virtually no deactivation, at 2,000 p.s.i.g., is observed with the molybdenum catalysts. For the cobalt-molybdenum and nickel-molybdenum catalysts, the deactivation rates were 19 F./b.p.p. and 25 F./b.p.p., respectively. Further investigations into the problem stemming from the fact that the most active hydrorefining catalyst has the lowest degree of stability, indicated that the stability, as above defined, of the nickelmolybdenum catalyst, for example, was greatly improved when processing hydrocarbon charge stocks containing not more than 2.0% by weight of sulfur. Furthermore, substantially no deactivation, of the nickel-molybdenum catalyst, was observed at charge stock sulfur concentrations of about 1.5% by weight, with the intended product sulfur level at 1.0% by weight.

The present invention is founded upon the discovery that a catalyst containing a zinc component and a Group VI-B component, for example molybdenum, experiences little activity decline when processing high sulfur-containing black oils to a sulfur concentration below about 2.0% by weight and, furthermore, effects considerable hydrogenation of the heavier material. Therefore, the traditional nickel-molybdenum, or cobalt-molybdenum, can be utilized in the second stage of a two-stage process wherein the zinc-molybdenum catalyst is employed in the first conversion zone to decrease the sulfur concentration to a level below about 2.0% by weight. With respect to the initial conversion zone, a preferred target sulfur level is in the range of about 1.35% to about 1.65% by weight.

The slight sacrifice made with respect to the initial catalyst activity in the first conversion zone is clearly overshadowed by the benefits accruing with respect to stability. Furthermore, a comparison of catalyst stability at the high sulfur level of black oils indicates that the maximum catalyst bed temperature of the nickel-molybdenum catalyst very rapidly increases to the initial maximum temperature of the zinc-molybdenum catalyst.

The catalyst disposed in the first reaction zone, intended for the initial processing of the black oil, contains from about 1.0% to about 10.0% by weight of a zinc component and from 4.0% to about 30.0% by weight of a molybdenum, or tungsten component, calculated as the elemental metals These metallic components are combined with a porous carrier material, containing alumina, which may be either amorphous, or zeolitic in character. The second stage catalyst contains from about 1.0% to about 10.0% by weight of a nickel, or cobalt component, and from about 4.0% to about 30.0% by weight of a molybdenum, or tungsten component, again calculated as if existing as the elemental metals. The second stage active components are also combined with a porous carrier material, preferably containing silica, and which may also be either amorphous, or zeolitic. Since neither the method of catalyst preparation, nor the ultimate form of the catalyst particles, with respect to either conversion zone, is an essential feature of my invention, further discussion thereof is not believed necessary herein. However, one suitable method of catalyst preparation involves impregnating a pre-formed carrier material, for example, spherical particles, with an aqueous solution of suitable soluble salts of the desired metal. Such suitable salts include molybdic acid, ammonium molybdate, tungstic acid, ammonium tungstate, nickel chloride, cobaltous chloride, nickel nitrate hexahydrate, cobalt nitrate hexahydrate, zinc chlorate, zinc chloride, zinc acetate, zinc nitrate trihydrate, zinc nitrate hexahydrate, zinc sulfate, etc.

Considering first the porous carrier material, it is preferred that it be an adsorptive, high-surfce area support. With respect to the first conversion zone, a preferred carrier material contains alumina, and with respect to the second conversion zone, a preferred carrier material contains silica. Suitable carrier materials are selected from the group of alumina-containing amophous refractory inorganic oxides including alumina, in and of itself, and in admixture with titania, zirconia, chromia, silica, magnesia, boria, for example, alumina-silica, alumina-silicazirconia, alumina-silica-boron phosphate, etc. When the carrier material constitutes a combination of alumina and silica, the concentration of the latter is in the range of about 10.0% to about 90.0% by Weight. In many applications of the present invention, the carrier material will consist, at least in part, of a crystalline aluminosilicate. This may he naturally-occurring, or synthetically-me pared, and includes mordenite, faujasite, Type A or Type U molecular sieves, etc. One common method of preparing a crystalline aluminosilicate constitutes mixing solutions of sodium silicate, or colloidal silica, and sodium aluminate, permitting the solutions to react to form a solid crystalline aluminosilicate. Another method is to contact a solid inorganic oxide from the group of silica, alumina and mixtures thereof with an aqueous treating solution containing alkali metal cations (preferably sodium) and anions selected from the group of hydroxyl, silicate and aluminate, and permit the solid-liquid mixture to react until the desired crystalline aluminosilicate has been formed. In addition to the foregoing, the carrier material may comprise a combination in which the zeolitic material is dispersed within an amorphous matrix, the latter being alumina, silica, or silica-alumina.

Following the formation of the catalytic composite, by whatever means desired, it will generally be dried at a temperature in the range of about 200 F. to about 600 F., for a period of from one-half hour to about 24 hours, and finally calcined at a temperature of about 700 F. to

about 1200 F., in an atmospher of air, for a period of about 0.5 to about ten hours. When the carrier material comprises a crystalline aluminosilicate, it is preferred to limit the calcination temperature to a maximum of 1000 F.

Although not essential to successful desulfurization, a halogen component may be combined with the other components of the catalytic composite. Although the precise form of the chemistry of association of the halogen component with the carrier material and metallic components is not accurately known, it is customary in the art to refer to the halogen component as being combined with the carrier material or with the other ingredients of the catalyst. The halogen may be either fluorine, chlorine, iodine, bromine, or mixtures thereof, with fluorine and chlorine being particularly preferred. The quantity of halogen is such that the final catalytic composite contains about 0.1% to about 3.5% by weight, and preferably from about 0.5% to about 1.5% by weight, calculated on the basis of the elemental halogen.

Prior to its use in the desulfurization of hydrocarbons, the resultant catalytic composite may be subjected to a substantially water-free reduction technique. Substantially pure and dry hydrogen (less than about 30.0 vol. ppm. of water) is employed as the reducing agent. The calcined composite is contacted at a temperature of about 800 F. to about 1200 F., and for a period of about 0.5 to about hours. This reduction may be performed in situ prior to introducing the charge stock.

Additional improvements are generally obtained when the reduced composite is subjected to a pre-sulfiding operation for the purpose of incorporating therewith from about 0.05% to about 0.5% by weight of sulfur, on an elemental basis. The pre-sulfiding treatment is effected in the presence of hydrogen and a suitable sulfur-containing compound such as hydrogen sulfide, low molecular weight rnercaptans, various organic sulfides, carbon disulfide, etc. One technique involves treating the reduced catalyst with a sulfiding gas, such as a mixture of hydrogen and hydrogen sulfide having about 10 mols of hydrogen per mol of hydrogen sulfide, at conditions selected to effect the desired incorporation of sulfur. Pre-sulfiding may also be effected in situ by way of charging a relatively lowboiling hydrocarbon feed containing sulfurous compounds.

In accordance with my invention, the hydrocarbon charge stock and hydrogen are contacted with a catalyst of the type described above in a hydrocarbon conversion zone. The contacting may be accomplished by using the catalyst in a fixed-bed system, a moving-bed system, a fluidized-bed system, or in a bath-type operation. In view of the risk of attrition loss of the catalyst, it is preferred to use a fixed-bed system. In this type of system, a hydrogen-rich vaporous phase and the charge stock are preheated by any suitable heating means to the desired initial reaction temperature, the mixture being passed into the conversion zone containing the fixed-bed of the catalytic composite. It is understood, of course, that the hydrocarbon conversion zone may consist of one or more separate reactors having suitable means therebetween to insure that the desired conversion temperature is maintained at the entrance to one or more catalyst beds. The reactants may be contacted with the catalyst in either upward, downward, or radial fiow fashion, with a downward/radial flow being preferred.

The operating conditions imposed upon the reaction zone, or zones, are primarily dependent upon the charge stock properties and the desired end result. However, these conditions will include a maximum catalyst bed temperature, for the catalyst disposed in the first reaction zone, in the range of about 600 F. to about 900 F. With respect to the second reaction zone, the maximum catalyst bed temperature will be in the range of about 550 F. to about 850 F., and about 50 F. lower than the temperature of the catalyst in the first reaction zone.

Other operating variables include a pressure of from about 400 to about 5,000 p.s.i.g., an LHSV of about 0.1 to about 10.0 and a hydrogen concentration of about 1,000 to about 50,000 s.c.f./bbl. Desulfurization reactions are generally exothermic in nature, and an increasing temperature gradient will be experienced as the hydrogen and feed stock traverse the catalyst bed. In order to insure that the catalyst bed temperature does not exceed the maximum allowed, conventional quench streams, either normally liquid or normally gaseous, may be introduced at one or more intermediate loci of the catalyst bed. In some situations, a heavy hydrocarbonaceous material is intended for hydrorefining, accompanied by partial conversion into lower-boiling hydrocarbon products. A portion of the normally liquid product efiluent boiling above the end boiling point of the desired product will generally be recycled to combine with the conversion zone charge stock. In this type of process, the combined liquid feed ratio will be within the range of about 1.1 to about 6.0.

ILLUSTRATIVE EXAMPLE Specific operating conditions, processing techniques, particular catalytic composites and other individual process details will be given in the following description of my invention. In presenting this illustration, it is not intended that the present invention be limited to the specifics, nor is it intended that a given process be limited to the particular operating conditions, catalytic composite, processing techniques, charge stock, etc. Therefore, it is understood that the present invention is merely illustrated by the specifics hereinafter set forth.

A traditional desulfurization catalyst was prepared by impregnating calcined alumina-silica spheres, containing 88.0% by weight of alumina, with nickel nitrate hexahydrate and molybdic acid (85.0% molybdenum trioxide) in amounts required to result in a final composite containing 1.8% by weight of nickel and 16.0% by weight of molybdenum, calculated as the elements. This catalyst was used to process a reduced crude oil having a gravity of 10.2 API. Other charge stock properties include an initial boiling point of 590 F., a 30.0% volumetric distillation temperature of 859 F. and a 55.0% volumetric distillation temperature of 1030 F. The charge stock contained 5.2% by weight of sulfur, 2,900 ppm. by weight of nitrogen, 9.1% by weight of heptane-insoluble asphaltenes and 87 p.p.m. by weight of nickel and vana dium. Operating conditions were a pressure of 1,900 p.s.i.g., an LHSV of 0.8 and a hydrogen concentration of 5,000 s.c.f./bbl.

At a maximum catalyst bed temperature of 750 F., 1.0% by weight of product sulfur was achieved; the catalyst life at this point was about 0.5 b.p.p. (barrels of fresh feed per pound of catalyst disposed in the conversion zone). At a catalyst life of 1.8 b.b.p., the catalyst temperature had been increased to 775 F., indicating a deactivation rate of 193 F./b.p.p. The operation was terminated at a catalyst life of 3.5 b.p.p. and a catalyst temperature of about 825 F., then indicating a deactivation rate of about 25.0 F./b.p.p.

A second catalyst was prepared by impregnating 82.5 grams of spherical alumina-silica particles 12.0% by weight of silica) with 18.16 grams of molybdic acid dissolved in 50 cc. of water and 23 cc. of 28.0% by weight ammonia, and 18.81 grams of zinc nitrate hexahydrate dissolved in 20 cc. of water. Following impregnation and drying in a rotary drier at about 225 F., the spheres were calcined for one hour at a temperature of 1100 F. Analyses indicated 10.4% by weight of molybdenum and 4.1% by weight of zinc.

The reduced crude was processed over a fixed-bed of the zinc-molybdenum catalyst at a pressure of 2,000 p.s.i.g., an LHSV of 1.6 and a hydrogen concentration of 5,000 s.c.f./bbl. During the first 25 hours of operation, for lineout purposes, the maximum catalyst temperature was maintained at 711 F.; the product sulfur level was 3.08%

by weight, and no deactivation was observed. From 25- 227 hours, with the maximum catalyst temperature virtually constant in the range of 758 F. and 762 F., the sulfur concentration steadily decreased to a level of 1.63% by weight. The following Table I presents sulfur analyses, on the product effluent, taken periodically during the 18- 227 hours of operation.

TABLE I.-PRODUCT SULFUR ANALYSES Time period, hours: Sulfur, Wt percent At 227 hours of on-stream operation, an upset necessitated a shut-down of the unit. Daily data incicated that the zinc-molybdenum catalyst performed exceptionally well in comparison to the traditional nickel-molybdenum catalyst. Over the initial 227 hours of operation, or a catalyst life of 1.29 b.p.p., no observable deactivation was evident. Further, the desulfurization response of the zinc-molybdenum catalyst to temperature was 0.275% sulfur/ F., as compared to 0.10% sulfur/ 10 F. for the nickel-molybdenum catalyst.

In view of the performance of this catalyst, and since no apparent damage, as a result of the upset, could be observed by visual examination, it was reloaded into the reaction zone, and the operation was continued. During the first 199 hours, or 1.19 b.p.p. of additional catalyst life, the maximum catalyst temperature only varied between 757 F.-760 F. with the sulfur level decreasing from 1.66% to 1.52% by Weight. At this point, the LHSV was halved to a level of 0.8, and the operation continued to a duration of 511 hours. A pump failure required a second unit shut-down; however, since the catalyst again indicated no observable damage, it was again reloaded, and the operation continued at the lower space velocity. An additional 316 hours of operation followed, and the results are summarized in the following Table 11, being inclusive of those results above described.

TABLE II.-PERFO RMANCE OF ZINC-MOLYBDEN UM CATALYST Catalyst Sulfur, Catalyst temp. weight life,

On-stream hours LHSV F.) percent b.p.p.

TABLE TIL-CARBON ANALYSES Nickel- Zinc Catalyst molybdenum molybdenum Catalyst life, b.p.p 3. 5 4. 4 Carbon, weight percent:

T 10.5 no

Middle 16. 3 7. n

TABLE IV.CHARGE STOCK ANALYSES Charge Stock A B C D Gravity, API 17. 9 18. l 17. 6 17.5 Sulfur, Weight percent 1. 60 1. 46 1. 50 1. 48 Initial boiling point 528 510 522 525 10% 680 700 702 706 30% 820 845 850 857 50%. 933 960 968 964 70% l 1,078 1, 085 1, 088 1, 084

The results of this operation, indicating no observable catalyst deactivation, are summarized in the following Table V.

TABLE V.-NICKEL-MOLYBDENUM CATALYST RESULTS Sulfur,

On-stream Catalyst weight Charge Stock hours temp. F.) percent The total catalyst life was 1.78 b.p.p., and it is readily ascertained that the deactivation rate is ni-l. Thus, the benefits afforded through the use of the present combination process are clearly indicated by the foregoing illustrative example.

I claim as my invention:

1. A combination process for processing a black oil containing more than 2.0% by weight of sulfur to obtain a lower-boiling product containing less than about 1.0% by weight of sulfur, which comprises the steps of:

(a) reacting said oil with hydrogen, in a first reaction zone, at a temperature in the range of 600 F. to about 900 F. selected to convert sulfurous compounds into hydrogen sulfide and a first hydrocarbon stream containing from 1.0% to 2.0% by weight of sulfur, and in contact with a first catalyst composite of an alumina carrier, a zinc component and a Group VI-B component; and,

(b) reacting said first hydrocarbon stream with hydrogen, in a second reaction zone, at temperature in the range of 550 F. to about 850 F. selected to convert additional sulfurous compounds into hydrogen sulfide and a second, hydrocarbon stream containing less than about 1.0% by weight of sulfur, and in contact with a second catalyst composite of a silica carrier, a nickel or cobalt component and a Group VI-B metal component.

2. The process of claim 1 further characterized in that said first catalyst is a composite of an amorphous alumina carrier, from about 4.0% to about 30.0% by weight of a molybdenum, or tungsten component, and from about 1.0% to about 10.0% by weight of a zinc component.

3. The process of claim 1 further characterized in that said second catalyst is a composite of a porous silica carrier, from about 4.0% to about 30.0% by weight of a molybdenum, or tungsten component, and 1.0% to about 10.0% of a nickel, or cobalt component.

4. The process of claim 3 further characterized in that said second catalyst carrier is an amorphous composite ofl alumina and about 10.0% to about 90.0% weight s11ca.

5. The process of claim 3 further characterized in that said second catalyst carrier includes a crystalline aluminosilicate.

6. The process of claim 1 further characterized in that the maximum temperature in said second reaction zone is at least about 50 F. lower than the maximum temperature in said first reaction zone.

References Cited UNITED STATES PATENTS 1,932,174 10/1933 Gaus et a1. 20889 2,969,316 1/1961 Stanford et a1. 20889 10 3,297,563 1/1967 Doumani 208210 3,457,161 7/1969 Tulleners 208210 FOREIGN PATENTS 5 773,173 4/1957 England 208210 901,332 7/1962 England 208--2l0 DELBERT E. GANTZ, Primary Examiner G. L. CRASANAKIS, Assistant Examiner U.S. Cl. X.R. 252-468; 208216 

